I'm actually already dealing with this myself- my old setting that I used for my 3.0/3.5 long-running epic campaign featured advanced technology and some of its consequences; for example the world has six equatorial space elevators linked to an immense ring-shaped station at the geosynchronous orbital position. So in updating the setting to PF rules, I've been looking back through Dragonstar as one of the sources to figure out what to do.

Gunslinger I'm already planning to make at least one Archetype focused on using advanced-tech weapons such as laser pistols; it's obvious that such an Archetype should exist if Gunslingers exist at all. More than one Archetype may be possible to squeeze out here, though I haven't delved deeply enough yet to be sure.

An issue you didn't touch on is gravity- and more specifically, microgravity and how to handle freefall. I decided to do it by taking the old Freefall skill from Dragonstar and fold it into PF's Fly skill. EDIT: Also, I almost forgot, there needs to be a Freefall condition to take into account the penalties associated with going out of control in a microgravity situation. The fun part about doing it this way is, you can make spells which inflict the condition upon people- even old favorites like Reverse Gravity might be retrofitted to include it. Other rules regarding gravity can mostly be ported over unchanged, as far as I've been able to tell.

Vehicle rules introduced in Ultimate Combat may need serious updates to deal with starships, particularly technological drives. I haven't gotten to this myself, yet, so don't have any solutions of my own to list here.

Basic idea is that Dragonstar encounters Forgotten Realms "as is". You could do a similar thing for Golarion, then no changes are needed to the Gunslinger, maybe the abilities just don't work with beam weapons?

The biggest thing I would think that would need to be thought and converted would be the pantheons/gods of Pathfinder and how those relate to the Unification Church

I love Dragonstar and I love the idea of Integrating it with Pathfinder!

I'm actually already dealing with this myself- my old setting that I used for my 3.0/3.5 long-running epic campaign featured advanced technology and some of its consequences; for example the world has six equatorial space elevators linked to an immense ring-shaped station at the geosynchronous orbital position. So in updating the setting to PF rules, I've been looking back through Dragonstar as one of the sources to figure out what to do.

Gunslinger I'm already planning to make at least one Archetype focused on using advanced-tech weapons such as laser pistols; it's obvious that such an Archetype should exist if Gunslingers exist at all. More than one Archetype may be possible to squeeze out here, though I haven't delved deeply enough yet to be sure.

An issue you didn't touch on is gravity- and more specifically, microgravity and how to handle freefall. I decided to do it by taking the old Freefall skill from Dragonstar and fold it into PF's Fly skill. EDIT: Also, I almost forgot, there needs to be a Freefall condition to take into account the penalties associated with going out of control in a microgravity situation. The fun part about doing it this way is, you can make spells which inflict the condition upon people- even old favorites like Reverse Gravity might be retrofitted to include it. Other rules regarding gravity can mostly be ported over unchanged, as far as I've been able to tell.

Vehicle rules introduced in Ultimate Combat may need serious updates to deal with starships, particularly technological drives. I haven't gotten to this myself, yet, so don't have any solutions of my own to list here.

I forgot about gravity--that's another good one. I can't recollect Dragonstar's rules for variant gravity but if I had to improvise some quick pre-game rules from scratch they would look like this.

Spoiler:

Note: These rules are not meant to serve as a scientific treatise but are only meant to simulate the effects of gravity well enough to allow suspension of disbelief for the layman player. If you want to try to calculate how much momentum shooting an arrow will give a creature in a zero-g environment, don't let me try to discourage you, but bear in mind all the factors that would have to go into a realistic version of such a calculation--you would have to calculate average values for the mass the arrow, the power efficiency of the bow, wind resistance effects, and the average mass of a player character (and if you wanted to have monsters and NPCs perform the same stunt, they come in an even greater range of masses, because a Huge creature would gain less from a bowshot than a Small one.

GRAVITY LEVELS--DEFINITIONS

Gravity environments range in strength from 0 to 10. A gravity level of 0 denotes the absence of gravity. Gravity in the range of 1 to 3 is considered "microgravity". Gravity of strength 4 to 6 is considered "normal" and imposes few penalties on creatures acclimated to life on a conventional planetary surface. Gravity of a strength from 7 to 9 is found on super-Earths, in the deep atmospheres of gas giants, and in high acceleration environments (such as experienced by fighter pilots) and represent the limits of survivability for mortal creatures. Gravity strength 10 represents any extreme light-bending gravity field generated by such objects as neutron stars, black holes, Spheres of Annihilation, and Implosion spells.

Antigravity, where it exists, would be represented by a negative number of the same magnitude as a normal gravity field of equal strength.

MOVEMENT

Normal overland movement in a gravity environment of 3 or less requires making a Climb, Swim, Acrobatics, or Fly check* for those not acclimated to the variant gravity or untrained in moving around in it. If a creature is physically incapable of performing any of these (for example, being in free fall in vacuum with no solid surfaces in reach), they gain the free-floating condition (lose dodge bonuses and Dexterity to AC and Reflex saves, move actions are limited to worn/carried equipment)?

*Free-floating movement in a freefall environment

Spoiler:

In freefall, Fly checks can be made through the use of worn/carried equipment. For example, throwing a rock, shooting an arrow, or discharging a firearm in a certain direction will cause you to move very slightly in the opposite direction. Objects and rates of movement are as follows.

Throwing a minor object (anything with a weight of "—"): 5 ft per object thrown, per hour

Shooting a bow, crossbow, or similar hand-drawn weapon: 50 ft per shot, per minute (5 ft per round)

Discharging a personal firearm or firing a ballista: 500 ft per shot, per minute (50 ft per round)

Note that one can throw/shoot/fire multiple objects to increase one's speed in a given direction, or reduce it (by aiming in the direction of movement).

If a creature in freefall needs to propel himself toward a specific point (such as the door of an airlock or toward another creature or a weapon in freefall), he must make a Wisdom check to accurately propel himself in the appropriate direction; DC is equal to object's touch AC +2 per 10 feet of distance. If the creature fails the Wisdom check, he will miss the target's square by 5 feet per point missed.

RESILIENCE

Variant gravity can have an influence on how far a creature can run, swim, or perform other stressing manual labor before it becomes fatigued or exhausted.

Walking, hustling, or forced marching in a high-gravity environment (strength 6 to 9) causes trouble for creatures acclimated to a lighter gravity.

6: May walk 4 hours without penalty, each hour of forced march imposes a Con check (DC 12, +2 per extra hour). May hustle for one half-hour without taking nonlethal damage, and then must make a Strength check (DC 12) every ten minutes to continue hustling.

7: May walk 1 hour without penalty, every half-hour of forced march imposes a Con check (DC 14, +2 per extra half-hour). May hustle for ten minutes without taking nonlethal damage, and then must make a Strength check (DC 14) each minute to continue hustling.

8: May walk ten minutes without penalty, every ten minutes of forced march imposes a Con check (DC 16, +2 per extra ten minutes). May hustle for one round without taking nonlethal damage. A Strength check (DC 18) is required each round to continue hustling.

9: May walk 1 round without penalty, each round of forced march imposes a Con check (DC 18 or more, +2 per round). Hustling for one round deals 1 point of nonlethal damage each round. A Strength check (DC 20) is required each round to continue hustling.

(Creatures acclimated to low-gravity or zero-gravity will suffer similar problems in a moderate-gravity environment.)

FALLING DAMAGE

Falling damage is attenuated by gravity level, which is represented by stepping falling damage dice up or down (for example, rolling d4's instead of d6's) and by increasing the falling increment of damage dice. The usual damage cap of 20 falling-damage dice applies only to falls in within an atmosphere, but in an airless environment this damage cap does not apply and falling damage is allowed to increase without limit. For all other falling-damage rules (as listed here: Environment), make the following substitutions:

**Damage from pushed, thrown, and shot objects in a freefall environment

Spoiler:

These objects follow the same rules as for improvised weapons. Very large objects (such as large cargo containers) can be used as (very slow, 5 ft/round) improvised ranged weapons. A creature can push an object of a weight up to the push/drag value for their Strength score to deal damage as an improvised weapon of its size, but can only target an unaware or helpless creature who could be caught and crushed against another solid surface by the heavy object. (Anyone else will have plenty of time to get out of the way or will simply be pushed out of the way.)

* * * * * * * * * * * * * * * * * * * *

Also, Salthorae's mention of Distant Worlds reminds me about teleportation and the 9th-level spell Interplanetary Teleport (which actually appears in Inner Sea World Guide and Ultimate Magic rather than DW). As written, the spell seems to allow even inter-stellar teleportation, something which had been expressly forbidden in the original Dragonstar setting. This issue can be resolved however by retroactively stating that

The actual gravity rules from Dragonstar are pretty simple. Changes to creatures' physiology were handled by templates introduced in the Galactic Races Guide, for Low and High Gravity (they didn't go beyond those). Sure, it's less realistic, but it's easy to remember and implement, and not a bad approximation overall.

The key is the seven types of gravity with rules designations: Earth gravity is Standard and is assumed to be the baseline for pretty much every base game world; of course, if the GM wants to start a game on a higher or lower gravity planet, he or she is free to do so but that changes the way the game works as per the gravity rules.

Low gravity goes from 0.5 to 0.8 G. Very Low goes from 0.1 to 0.5 G, anything below 0.1 G is considered Microgravity.

On the other end of the scale, High gravity runs from 1.2 to 2.0 G, Very High from 2.0 to 4.0, and anything above 4.0 is Extreme.

Now, armed with these gravity designations, the Tables say the following rules changes happen:

The ability score modifiers are directly added or subtracted from the character's actual ability score; a character whose STR is reduced to 0 can't move at all. A character whose DEX is reduced to 0 by higher gravity is in essentially the same boat, but having DEX reduced to 0 by low gravity has a different effect: the character can flail about wildly, but is completely incapable of coordinated or controlled movement.

For PF, I took this last point to mean the character is in an effectively permanent Freefall condition; I defined the Freefall condition as follows (this text closely approximates text from the Dragonstar Freefall skill explaining what happens when you fail a check):

Freefall: A creature with the Freefall condition is spinning and drifting wildly out of control, in a zero-gravity or microgravity environment. Creatures in Freefall lose their DEX bonus and all Dodge bonuses to AC and CMD, and opponents get a +4 circumstance bonus on attack rolls and combat maneuver checks against Freefalling creatures. Freefalling creatures cannot take move actions, except attempts to regain control of themselves using Fly checks, and cannot make attacks of opportunity (though they can still make normal attacks if they happen to have targets in range). Freefalling creatures suffer a -4 penalty on melee attacks, and a -6 penalty on ranged attacks. Creatures in Freefall must make Concentration checks in order to cast spells or manifest psionic powers (DC equals the original Fly check DC that gave them the Freefall condition), Finally, creatures in Freefall suffer a -6 penalty on all skill or ability checks based on mental ability scores (INT, WIS, or CHA) because of disorientation.

Added text to the Fly skill, I have here:

In addition to its uses in a standard-gravity environment, the Fly skill is used whenever you need to move or maneuver in a microgravity or zero-gravity environment. Even simple movements under such gravity conditions are challenging for most creatures born in standard or higher gravity fields, and you must retrain your body to adjust to them.
Check: Whenever you try to make any sort of complicated or violent motion in a microgravity or zero-G environment, you must make a Fly check. If the check succeeds, then nothing else happens; if it fails, then you lose control over your position and movement after the action is completed, gaining the Freefall condition. The Fly check does not determine the results of the action itself, only whether you are able to avoid Freefall.

Attacks with all weapons except ranged energy weapons (which have no recoil) require a Fly check for this purpose, as do all Reflex saving throws. Being struck by an attack also usually requires a check to retain control of your position, though some attacks which do not produce a physical or kinetic result (such as a hit from a laser, or being burned by a Fireball spell assuming the Fly check triggered by your Reflex save succeeded) do not. Casting spells or manifesting psionic powers generally does not produce recoil or involve sudden/violent motions, so those actions do not incur Fly checks to avoid spinning out of control.

If you fail a Fly check to retain control in a microgravity or zero-G environment, you gain the Freefall condition, spinning and drifting wildly out of control. [here the text for the Freefall condition is copied.]

While in Freefall, you can take a move action (which provokes attacks of opportunity) to regain control of your body and position, and lose the Freefall condition. This requires another Fly check against the same DC as the check that originally failed and gave you the Freefall condition. If you have a convenient nearby surface to anchor against, you gain a +5 circumstance bonus on the check.

Action: Fly checks for moving in microgravity and zero-G conditions are always made as part of another action, and do not require actions in their own right.

Try Again: Yes, to regain control of yourself after an earlier failed check.

Special: If you have a solid object to brace yourself against and/or anchor yourself to, you gain a +5 circumstance bonus on Fly checks made to avoid Freefall.

The way I figure it, if you're swimming in water in a microgravity environment, it won't be that different from swimming in a gravity environment- the water/liquid density will help you move assuming you know how to move within it in the first place. So the above rules would only be used in air or a vacuum, and thus, one only needs to consider the Fly skill for microgravity.